Conventional mechanisms for retaining and automatically releasing safety equipment at sea includes a rope or strap wound around the equipment with one end affixed to a support and the other fastened to a release mechanism. Upon a trigger signal from a sensing mechanism such as a diaphragm sealing a closed chamber, the release mechanism releases or cuts one end of the strap. The equipment then is designed to float free of the craft. Problems may be experienced, however, with devices which use a cutting mechanism for the release of equipment, such as European Patent Office Publication No. 0 198 805 by Hermansson. If such a mechanism cuts through one end of the strap or rope, it may fail to cut cleanly, or once cut, the strap or rope may become caught in the mechanism itself. Such a possibility is understandable considering that the end being cut must be held securely for the cutting procedure. Alternatively, an external object such as a line or other object may lie across the strap or cord near the end to be released preventing the equipment from being freed.
Where release mechanisms are used for the automatic release of lifeboats or radio beacons, it is desirable for the release mechanism to be sensitive to an increase in water pressure, usually to a predetermined level, but immune to increases in air pressure, such as those caused by increases in temperature. Increases in air pressure may cause accidental activation of a release mechanism where the mechanism comprises a diaphragm separating two air chambers, and provisions have not been made for the equalization of the external air pressure with the internal air chamber pressure. U.S. Pat. No. 2,839,767 of Sieverts and U.S Pat. No. 3,075,208 of Mercer and Dewar describe sealed air chambers which are sensitive to fluctuations in air pressure occasioned by temperature changes, and hence, are unreliable for uses where only water pressure sensitivity is desired.
Japanese Patent No. 61-16191 describes a release mechanism which is immune to changes in temperature and air pressure, but may become jammed as only one end of its strap is released. U.S. Pat. No. 2,360,848 of Bryant also describes a release mechanism sensitive to changes in water pressure while immune to changes in air pressure; however, this mechanism may fail to release due to undesired frictional forces. Bryant's invention describes a configuration where two plate-like sections directly exert undesired biasing forces against a pin on which release is dependent. These biasing forces cause sufficient friction that the pin is either unable to reliably activate the release mechanism, or delays release until a water pressure greater than the predetermined level is attained. Both U.S. Pat. Nos. 2,839,767 and 3,075,208 seek to avoid these undesired biasing forces, but are sensitive to air pressure changes.
Accordingly, it is an object of the present invention to provide an improved, more reliable automatic release mechanism which is sensitive to a change in water pressure to a predetermined level, but immune to changes in air pressure or temperature. It is a further object of the invention to provide a release mechanism which completely releases a strap or cord from the support object.